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To explain a little more, I drilled and tapped for 4mm metric bolts into my verandah posts and the bolts stuck out horizontally to which I wound the enamelled wire to and then applied the tape to one side first using the guide as I went along, then applied thee other side of the tape to seal it off and like Ian bout 6m was it

I went to all that trouble but could never get the hang of setting up the testing equipment to find out how my coils were(fast)

Hi guys .While learning to construct coils i have noticed how the coil to shield capacidence can be reduced a lot by increasing the spacer between coil and shield . Could this have a reverse effect on the coil speed by increasing the ground capacidence thanks

I don't know about influencing coil speed. Maybe some more experienced can explain.

But by increasing spacing between bundle and shield, a greater amount of shielding is used - in the case of wrap-around type shielding.. And that would lead to greater coil-shield capacitance and ground to shield capacitance too. So use lower strand count in the shield. I think Ron experienced this when shielding larger coils, and found things worked out by reducing capacitance/shield strand.

I wonder what the spec for shielding is on the new generation of commercial flat wound coils ? Whats the biggest one they make ?

The less capacitance the faster the coil shown by the self resonance both methods of shielding have their uses for your coil use bolts with 1.2 mm pitch thread and if it were me I would try for around 10 mm coil bundle to shield spacing.

When I made Stefan's shielding I made a standard shielding tape and soldered this to the coil and by trial and error by snipping one strand of wire at a time from the shielding, I checked this against depth and noise thru the phones and chose a happy medium

Problem for me was my test bed was nowhere near real life conditions and since I had already glassed the coil..i failed

When I made Stefan's shielding I made a standard shielding tape and soldered this to the coil and by trial and error by snipping one strand of wire at a time from the shielding, I checked this against depth and noise thru the phones and chose a happy medium

Problem for me was my test bed was nowhere near real life conditions and since I had already glassed the coil..i failed

Cheers Ron

Hi Ron,

You could have tried changing the coax to one with different specs. Seems like quite a challenge, building coils.

Hi After reading posts by authere on geotech regarding shieldi minlab coils using Stefarns methord and altering the strand count .Has anyone found a way to get a good strand count using the coil to sheild capacindence and could the coil to shield spacer thickness play a part in altering the strand count

Missed this one, I used to make my own coax which used the same wire as in the coil that I was making and then wrapped several rolls(six) of Teflon plumbing tape then spiral wound .15 wire until covered the Teflon, then heatshrink over that....I was told how to go about it by Digger

Alex,

From memory you had to keep the cap below 400 and by adding more shielding space would lower the cap so in some cercumstances you would have to increase the strand count to compensate but the main idea was to overall lower the cap to as low as possible...its all trial and error

Woody was working on this very thing and was using some sought of wire cloth or sheet but I didn't go there

I think Ian gave you optimum guidelines on strands and insulator spacing (a few posts above), for the size of the latest coil you were trying to build. You are asking a lot of questions, and I bet there must be a way to plug figures into a calculator to come up with recommended figures for a given shield type/coil-to-shield spacing/coil bundle thickness.

One important thing you should remember, is these words posted by Stefan...... "One further point , if you minimize the shield to coil capacitance without making an appropriate reduction in the Q then the coil will be noisy. ie to much coil gain." (
)

It will be interesting to hear detailed info on your success on any of your experiments.

Hello Ron,

Sounds like a good idea to use the continuation of the coil wire as the centre conductor for your coax. I guess you were trying to get rid of solder balls/joints.

But I think it makes for a harder job for a novice to make final fine tune "Q" adjustments to get the coil performing on hard ground. You could sleeve the conductor with varying thicknesses of insulating tube, and vary cable capacitance, but what about impedance/resistance fine adjustment ? Snip wires ? And end up with disconnected 20m long strands sitting inside the bundle ? This is advanced stuff. Most people interested in trying to build their own coils don't have the time,space or facilities to make their own tailored conductor wire.

At least if we use a separate length of coax, we can change it to another type with different capacitance and resistance to gauge differences in coil behaviour and response on hard ground. And save from throwing away a coil as being useless. If solder joints are a concern, then use ferrite beads. I'm just trying to look at this experience through the eyes of someone new to m/l coil construction. The whole experience can be littered with pitfalls.

Thanks Ron.Reading the posts between you and digger .On diggers 3 foot coil he found at wire spacings of 12mm the coil was quite and you found your 6 inch was quite with 20 strands .I thought based on a spoked wheel digger would have about 238 strands ,you may have 1.2 mm spacings on a 6 inch on a 20mm tape .and based on this i was going to try a see if the spacings increased like wheel spokes on a 12 inch coil im about to shield.Also like you i calculate the Q by formula , my first coil was 3.5 and a bit noisy my next 18 inch i dropped Q to 3.3 the same as the military coil it came with so far its an improvement .thanks again

It all became a bit too much for my poor little ole brainbox, I still have a quite a few unfinished coils for the simple reason of not being able to check the finished product. They are all in a box with their shielding wrapped around

I'll stick to finishing off my 5.8m ali boat, just got to finish welding the gunnals and chequer plate deck and a centre console, fit a motor and I'm out there